• Journal of Power System Engineering
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• v.20 no.2
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• pp.73-78
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• 2016

In this study, the performance characteristics of a high temperature heat pump dryer that is able to raise the air temperature up to $80^{\circ}C$ by using waste heat as heat source were investigated numerically. The main components of the heat pump dryer were modeling as a compressor, condenser, evaporator and expansion device, and R245fa was selected as refrigerant. Experiments were also conducted to validate the numerical data. As a result, when the evaporator air inlet temperature increased from $50^{\circ}C$ to $65^{\circ}C$, the numerical results of the hot air temperature at outlet and heat pump COP were about 8~11% and 5~8% higher than that of experimental ones, respectively.

• Journal of Power System Engineering
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• v.21 no.1
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• pp.24-29
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• 2017

Studies in liquid-vapor ejector, which performs a great efficiency in refrigeration cycle is highly concerned. This paper is based on basic refrigeration cycle and three ejector refrigeration cycles and the comparison and contrasts about when 6 different refrigerants are applied to such refrigeration cycles. All cycles had a percentage increase of COP from 4 to 74% when ejector was applied, and the source of increasement was the decrease of total work done due to ejector's pressure recovery function. When R-245fa is applied to cycle (d), results showed that COP was the most superior in such cycle, R-245fa showed high volume entrainment ratio in all cycles. Future studies in refrigeration cycles will require more knowledge and experiments on ejector's appliance to refrigeration cycles and the actuation of such functions.

• The KSFM Journal of Fluid Machinery
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• v.17 no.6
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• pp.5-12
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• 2014

Organic Rankine Cycle is widely used to convert the low-grade thermal energy to the electrical energy. However, usually available thermal energy is not supplied constantly. This makes hard to use positive displacement expanders. Hence, turbo-expander has merits to apply as an expander in ORC because it can operate well off-design points even though the mass flowrate is fluctuated. The thermal energy fluctuation causes the turbo-expander to operate in partial admission. In addition, supersonic nozzles are required so that the partially admitted turbine operates efficiently. In this study, R245fa was chosen as a working fluid of ORC. A design method and an analysis technique of supersonic nozzle based on R245fa were developed. The shape of the nozzle was designed by the characteristic method. The thermal properties within the nozzle were estimated and the predicted results were agreed well with the computed results.

• The KSFM Journal of Fluid Machinery
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• v.17 no.1
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• pp.12-21
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• 2014

An organic Rankine cycle was analyzed to work at the optimal operating point when the heat source is fluctuated. R245fa was adopted as a working fluid, and an axial-type turbine as expander on the cycle was designed to convert the heat energy to the electricity since the turbo-type expander works at off-design points better than the positive displacement-type expander. A supersonic nozzle was designed to increase the spouting velocity because a higher spouting velocity can produce more output power. They were designed by the method of characteristics for the operating fluid of R245fa. Three different cases, such as various spouting velocities, various inlet total temperatures, and various nozzle numbers, were studied. From these results, an optimal operating cycle can be designed with the organic Rankine cycle when the available heat source as renewable energy is low-grade temperature and fluctuated.

• The KSFM Journal of Fluid Machinery
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• v.18 no.4
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• pp.5-12
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• 2015

Several working fluids for Organic Rankine Cycle(ORC) were recommended by many researchers. However, the recommended optimal working fluids were not exactly same because the operating conditions of ORC and application were different. The major parameter to select the working fluid for ORC was the temperature of available thermal energy. In this study, low-grade thermal energy was used for the heat source for ORC and the appropriate working fluids were searched among 26 candidate working fluids. The requirements to be a working fluid for ORC were reviewed and the cycle analysis for simple cycle was conducted with $75^{\circ}C$ and $35^{\circ}C$ at the turbine inlet and exit, respectively. R600, R601, toluene were best candidates if the system could work without leaking the working fluid. Next, R236ea, R245ca, R245fa were recommended because they are not inflammable working fluids as well as better efficiency.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.9
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• pp.881-889
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• 2015

Ocean thermal energy conversion is an organic Rankine cycle that generates power using the temperature difference between surface water and deep water. This study analyzes the thermodynamic efficiency of the cycle, which strongly depends on the working fluid and the cycle configuration. Cycles studied included the classical simple Rankine cycle, Rankine cycles with an open feedwater heater and an integrated regenerator, as well as the Kalina cycle. Nine kinds of simple refrigerants and three kinds of mixed refrigerants were investigated as the working fluids in this study. Pinch-point analysis that set a constant pinch-point temperature difference was applied in the performance analysis of the cycle. Results showed that thermodynamic efficiency was best when RE245fa2 was used as the working fluid with the simple Rankine cycle, the Rankine cycles with an open feedwater heater and an integrated regenerator, and when the mixing ratio of $NH_3/H_2O$ was 0.9:0.1 in the Kalina cycle. If the Rankine cycles with an open feedwater heater, an integrated regenerator, and the Kalina cycle were used for ocean thermal energy conversion, efficiency increases could be expected to be approximately 2.0%, 1.0%, and 10.0%, respectively, compared to the simple Rankine cycle.